This invention concerns a lamp seal of functionally gradient material and a lamp, such as a mercury lamp, metal halide lamp or halogen lamp.
Functionally gradient materials are composed of mixed sinters of, for example, an electrically conductive material such as a metal and a non-conductive material such as an oxidation product of a metal. By varying the proportion of the conductive material in stage in a specified direction, it is possible to form a material that has a conductive portion where there is a high proportion of the conductive material as well as a non-conductive portion where there is a low proportion of the conductive material. The conductive and non-conductive portions make up a solid whole that is well-suited as a seal material that forms a current feed in lamp seals.
When this sort of functionally gradient material is used as a lamp seal, it is necessary for the electrical feed lead bar to pass through the functionally gradient material in order to provide electrical contact between the inside and outside of the lamp. For example, it is possible to make a through-hole for the lead bar from the end of the functionally gradient material in the direction of the build-up, or to make non-through lead bar holes in each end of the functionally gradient material and insert the lead bar into one of the holes.
However, if a lead bar made of a metal such as tungsten is simply inserted and fixed in place, the lead bar will be organizationally united with the insulative, inorganic component of the seal, which consists of silica, for example. The result of that is the occurrence of cracking in the seal, caused by the differences in the indices of thermal expansion of the two.
If, on the other hand, there is a space between the lead bar and the seal material, a material such as mercury that is sealed into the light-emitting tube of the lamp will penetrate that space. Condensation of that will cause variation in the operating characteristics of the lamp. To prevent that phenomenon, it is effective to form a layer of a metallic powder such as powdered molybdenum or a thin film of a high-melting-point metal around the outer periphery of the lead bar. By this means, the sealed-in substance can be prevented from penetrating the space and condensing, and at the same time cracking of the seal material is prevented.
However, the production process is complicated by the matter of forming a layer of a metallic powder or a thin film of a high-melting-point metal around the outer periphery of the lead bar. There is a further problem in that it is not possible to obtain a product having the desired characteristics.
This invention was made on the basis of the situation described above. Its purpose is to provide a lamp seal of functionally gradient material that does not incur cracking and so has adequate durability against aging.
An additional purpose of this invention is to provide a lamp using this lamp seal of functionally gradient material that has a thermally stable, air-tight construction, and that has stable operating characteristics and a long service life.
The lamp seal of functionally gradient material of this invention comprises a seal piece made of functionally gradient material and a lead bar that is fixed in this seal piece;
which seal piece comprises an inorganic layer with insulative properties and a number of mixed layers that are each mixtures of conductive inorganic materials and insulative inorganic materials, such that the proportion of conductive inorganic materials increases gradually in the direction of layering, there being a hole formed to extend in the direction of layering;
the lead bar being inserted into the seal piece and fixed in place with a sleeve-shaped metallic part made of a high-melting-point metal located in the space between the outer periphery of the lead bar and the hole in the seal piece.
In this lamp seal of functionally gradient material, the sleeve-shaped metallic part preferably consists of a metallic foil with a high melting point wrapped in a cylindrical shape.
The sleeve-shaped metallic part can also consist of a band of metallic foil with a high melting point that is wrapped in a spiral around the outer periphery of the lead bar.
It is preferable that the sleeve-shaped metallic part be present at least in the full region of the seal material in which the proportion of conductive inorganic material is 15 vol-% or less.
It is also preferable that the high-melting-point metal making up the sleeve-shaped metallic part be molybdenum or an alloy that is primarily molybdenum.
In addition, it is preferable that the sleeve-shaped metallic part be formed with a coating of rhenium, rhodium, platinum or an alloy thereof on the outer surface of the sleeve.
The lamp of this invention is characterized by having an air-tight structure by means of a lamp seal of functionally gradient material.